The present invention relates to an engine control system for increasing a fuel injection quantity at accelerating and changing, for example, an exhaust gas flow according to a driving status wherein an engine controls a fuel injection depending on an intake pressure.
In such an engine that the fuel injection quantity is controlled by an electronic device, an air flow meter and a hot wire air flow sensor are provided in an intake passage for detecting an intake air flow and determines the fuel injection quantity according to signals from the meter and the sensor. However, the air flow meter is large and therefore, it has a laying out disadvantage. Also, an intake resistance becomes large by the air flow meter and correspondence to the change of the intake air flow may be delayed easily.
As disclosed in the Japanese Patent Application Laing Open Gazette No. 59-15656, it is known that the fuel injection quantity is determined by a data map, etc. on the basis of an intake pressure detected by an intake pressure sensor (MAP sensor) for detecting a pressure inside an intake manifold on a downstream of a throttle valve.
Some engines include changing means for changing exhaust gas flow of an exhaust system depending on the driving status. For example, by diving one turbosupercharger at a low intake air flow and driving two turbosuperchargers at a high intake air flow, the efficiency of supercharging can be improved. In other words, the exhaust system is divided into two systems and a turbine of one of superchargers is provided on each system. The changing means change the exhaust gas flow by supplying the exhaust gas to both turbines or supplying the exhaust gas to only one turbine, which means the exhaust gas is shut out to flow to the another turbine.
In such an engines including changing means, a fuel injection control can be carried out on the basis of signals from the above intake pressure sensor. Also, in the fuel injection control, correctively increasing the fuel injection quantity for improving the efficiency at acceleration has been tried.
In some cases, both increasing fuel injection quantity means for correctively increasing the fuel injection quantity on the basis of the signal from the intake pressure sensor and the changing means for controlling the exhaust gas flow are provided together. However, the engine combustion may become worse by a fluctuation of an air fuel ratio when the exhaust gas flow is controlled under the fuel injection quantity is increased at acceleration.
In detail, the air fuel ratio is easy to fluctuate by the delay of fuel supplying during acceleration when the fuel injection quantity is increased. On the other hand, when exhaust gas flow is changed, an exhaust pressure (an exhaust gas pressure) is changed according to the change of the exhaust gas flow and the intake air charging of the engine is changed even the same intake pressure is maintained. Then, the fluctuation of the air fuel ratio occurs easier. Accordingly, when the exhaust gas pressure is changed by changing the exhaust gas flow under acceleration wherein the air fuel ratio fluctuates, the air fuel ratio may fluctuate more.
Also, a system of supercharging intake air to an engine by utilizing a dynamic effect of intake air encounters the same problem when the intake pressure is changed. For example, a volume part is provided on the intake system to gain a dynamic effect. In a specified engine speed region (tuning speed region), an intake negative pressure wave generated on an intake port according with the opening of an intake valve at an initial stage of intake air process of each cylinder is transmitted to an upstream side of an intake passage on a sonic speed, and the negative pressure wave is converted to a positive pressure wave at the above volume part. Thereafter, the positive pressure wave is transmitted to the downstream side of the intake pressure on a sonic speed through the same passage so as to reach at the same intake port at the last stage of the intake air process which is right before the intake valve is closed, and an intake air is compressed to a combustion chamber by the positive pressure wave in order to improve the charging efficiency.
At this time, in a wide range of engine speed, in order to gain the efficiency of supercharging by the above dynamic effect, the length of the intake passage is changed in several ways and by this change, the intake air flow is changed. When the intake air flow is changed, the intake pressure is changed according with it and the intake air charging to the engine is changed. Consequently, the air fuel ratio is easy to fluctuate. Thus, at acceleration of the engine, the air fuel ratio fluctuates greatly by the change of the intake pressure from changing of the intake air flow.
The objects of the present invention is to provide such an engine control system prevents that the fluctuation of air fuel ratio caused by delaying of fuel supply at acceleration of the engine and by the pressure change by the exhaust gas and intake air flow and improves the engine combustion at the acceleration.